The present invention relates to a new and improved construction of an apparatus for controlling the warp thread tension in a loom or weaving machine containing a back rest.
In its more particular aspects, the present invention specifically relates to a new and improved construction of an apparatus for controlling the wire threads tension by means of positionally displacing the back rest in the loom or weaving machine. The apparatus comprises at least one swivelling lever mechanism which includes at least one rocking lever carrying a shaft of the back rest and which swivelling lever mechanism is controlled by means of at least one cam plate or disc. The apparatus also possesses means effecting an additional warp thread tensioning by means of an additional positional displacement of the back rest during the start-up operation of the loom or weaving machine.
It is a purpose of an apparatus of the abovementioned type to cause, during the start-up operation of the loom or weaving machine, an additional warp thread tension so that the fabric start-up marks or irregularities are prevented which usually appear during the start-up operation of the weaving machines and which visibly reduce the quality of the woven fabric.
In an arrangement known, for example, from German Pat. No. 2,927,533, there is fastened for this purpose on the back rest shaft, an arm adjustable by means of a first swivelling lever. The back rest shaft is carried on rotatably mounted cantilevers, the rotary mounts of which are arranged in levers which are pivotable about a stationary axle. The levers are articulated by means of connecting rods with a further lever which is mounted on a shaft spring-loaded in its rotary direction. In this arrangement, the further lever or swivelling lever of this additional apparatus of the loom or weaving machine is connected with a swivel arm which is rotationally mounted on the spring-loaded shaft. The swivel arm, in turn, is in operative connection with an additional lever fixed to the shaft by means of a hooking apparatus. This hooking apparatus is controllable via an electromagnet such that, during the start-up operation, the back rest shaft is positionally changeable due to the entrainment of the additional lever by the rotationally mounted swivel arm.
Such an arrangement permits an additional positional displacement of the back rest to be superimposed during the start-up operation of the weaving machine upon the tension-controlling displacement of the back rest during normal operation while avoiding the separate auxiliary back rest used at that time in order to prevent the formation of the fabric start-up marks or irregularities. However, this is only realized by means of a technically highly complex apparatus.